Phenolic resin composition

ABSTRACT

An object of the present invention is to provide a phenolic resin composition which is stable against an environmental moisture change and, further, excellent in fast curing property, flexibility and heat resistance. According to the present invention, the phenolic resin composition, containing 70-97% by weight of a phenolic resin and 3-30% by weight of a silicone-based rubber component, which is characterized in that a ratio of an ortho-bonding to a para-bonding at a methylene bonding in the phenolic resin is 2-9 can be provided.

TECHNICAL FIELD

[0001] The present invention relates to phenolic resin compositions.More particularly, the present invention pertains to a phenolic resincomposition which is stable against an environmental moisture change andis excellent in fast curing, flexibility and heat resistance.

BACKGROUND OF THE INVENTION

[0002] A phenolic resin is relatively favorable in curing property,molding property and the like and a cured product thereof is excellentin electrical and mechanical characteristics so that the cured productthereof has widely been utilized for a molding material, a laminatedmaterial, a friction material for a disc brake pad and the like, a shellmolding material, a casting material, a foamed material and the like asa well-balanced material thereby allowing the cured product thereof tobe of an industrially valuable material.

[0003] However, the phenolic resin is liable to absorb moisture when anenvironmental moisture is changed and, once the phenolic resin absorbsthe moisture, a curing behavior thereof is changed such that a curingrate is accelerated whereupon, f or example, a yield of molded productsat the time of molding was deteriorated, qualities of the moldedproducts were varied from one another and the like. However, noeffective measure to solve these problems has actually been proposed.

[0004] Further, though the phenolic resin can be a binder which hasexcellent mechanical characteristics, electrical characteristics, heatresistance, adhesivity and the like, the molded product thereof has adrawback that it is inferior in flexibility and vibration absorption. Inorder to improve these performances, studies on modified phenolic resinshave actively been conducted. For example, among others, studies onoil-modified phenol resins, cashew-modified phenol resins,silicone-modified phenolresins, epoxy-modified phenolresins,melamine-modified phenol resins and the like have been conducted wherebysome of the above-described modified phenol resins are put in an actualuse.

[0005] To give one example of such usage, a first Japanese Patentlaid-open, namely, Japanese Patent Laid-Open No. 323080/1999, disclosesa method of producing a phenol resin composition in which a silicone gelbased on an addition reaction type silicone having from 10 to 500 of apenetration number is kneaded into a phenol resin by using a pressuremixer. However, though a modified phenol resin composition obtained bythis method has been improved in flexibility, vibration absorption andthe like to some extent, stability against the environmental moisturechange was insufficient.

[0006] Further, a second Japanese Patent laid-open, namely, JapanesePatent Laid-Open No. 071497/1999, discloses a rubber-modified phenolresin composition which is a phenolic resin composition containing aphenol resin which is a polycondensate of a phenol and an aldehyde andhas a ratio (o/p ratio) of an ortho-bonding to a para-bonding at amethylene bonding in the resin being from 1.0 to less than 4.5 and arubber component as essential components, in whichacrylonitrile-butadiene rubber (NBR) and an elastomer containing anacrylic acid ester are used as the above-described rubber component.

[0007] However, though such a rubber-modified phenolic resin compositionas described above has been improved in flexibility, vibrationabsorption and the like to some extent, heat resistance and stabilityagainst the environmental moisture change were insufficient. On thisoccasion, the o/p ratio described in the above-described Japanese Patentlaid-open, namely, the second Japanese Patent laid-open, is determinedby a ratio of absorbance of the ortho-bonding appearing in a range offrom 730 cm⁻¹ to 770 cm⁻¹ to that of the para-bonding appearing in arange of from 800 cm⁻¹ to 840 cm⁻¹ in an infrared absorption spectrum. Avalue of the o/p ratio obtained by this measuring method comes out lowerthan that obtained by a measuring method described in embodimentsaccording to the present invention. Specifically, a range of from 1.0 toless than 4.5 of the o/p ratio obtained by this measuring methodapproximately corresponds to that of from 0.4 to less than 2 of the o/pratio obtained by the measuring method described in the embodimentsaccording to the present invention.

[0008] Furthermore, a third Japanese Patent laid-open, namely, JapanesePatent Laid-Open No. 144106/2000, describes a rubber-modified high-orthophenolic resin for use as a binder for a non-asbestos-based frictionmaterial in which NBR is used as such a rubber component as describedabove and the ratio (o/p ratio) of the ortho-bonding to the para-bondingat a methylene bonding in a resin portion of the high-ortho phenol resinis 1.0 or more, and, preferably, from 1.0 to 4.5. However, though such arubber-modified phenolic resin as described above has been improved inflexibility, vibration absorption and the like to some extent, heatresistance and stability against the environmental moisture change wereinsufficient. On this occasion, the o/p ratio described in this JapanesePatent laid-open, namely, the third Japanese Patent laid-open, isdetermined by a same measuring method as in Japanese Patent Laid-OpenNo. 071497/1999, namely, the above-described second Japanese Patentlaid-open; therefore, in a same manner as in the second Japanese Patentlaid-open, a range of the o/p ratio described in this Japanese Patentlaid-open comes out lower than that of the o/p ratio according to thepresent invention.

DISCLOSURE OF INVENTION

[0009] In view of the above-described problems, an object of the presentinvention is to provide a phenolic resin composition which is stableagainst an environmental moisture change and excellent in fast curingproperty, flexibility and heat resistance.

[0010] Inventors of the present invention have found as a result of anintensive study that, when a resin composition comprising a phenolicresin and a rubber component as essential components is produced, theabove-described problems can be solved by using a resin in which a ratio(o/p ratio) of an ortho-bonding to a para-bonding at a methylene bondingin the phenolic resin is controlled to be in a specified range and,further, incorporating a specified quantity of a specified rubbercomponent thereto to achieve the present invention.

[0011] In other words, the present invention is a phenolic resincomposition, comprising from 70% by weight to 97% by weight of aphenolic resin and from 3% by weight to 30% by weight of asilicone-based rubber component, which is characterized in that a ratio(o/p ratio) of an ortho-bonding to a para-bonding at a methylene bondingin a phenolic resin is from 2 to 9.

[0012] As for a preferred aspect of the phenolic resin compositionaccording to the present invention, mentioned is such a resincomposition as described above in which a viscosity of a silicone-basedrubber is from 5000 mm²/s to 200000 mm²/s at 50° C. Further, mentionedis such a phenolic resin composition as described above which ischaracterized by being a compound of from 85% by weight to 99% by weightof an organopolysiloxane having a silanol group at each terminal of amolecule thereof and from 1% by weight to 15% by weight of acrosslinking agent for silanol condensation as the silicone-basedrubber.

[0013] As for the organopolysiloxane having a silanol group in eachterminal of a molecule thereof, mentioned is a compound which isexpressed by the following general formula (1):

[0014] wherein

[0015] R₁ and R₂ are same with or different from each other and eachindividually represents any one of a monovalent hydrocarbon group, analkyl group such as a methyl group, an ethyl group, a propyl group, abutyl group or the like, an aryl group such as a phenyl group, a xylylgroup or the like, and a halogenated monovalent hydrocarbon such as aγ-chloropropyl group, a 3,3,3-trifluoropropyl group or the like; and

[0016] n represents an integer of from 4 to 675.

[0017] Further, as for the crosslinking agent for silanol condensation,mentioned is a multifunctional silane compound in which three or morefunctional groups of at least one type selected from the groupconsisting of: an alkoxy group, an acyloxy group, a ketooxime group, analkenyloxy group, an aminooxy group and an amino group are directlybonded to a silicon atom.

[0018] The phenolic resin composition according to the present inventionmay contain from 3 parts by weight to 20 parts by weight ofhexamethylenetetramine based on 100 parts by weight of the resincomposition. Such resin composition is advantageously used as a binderfor a friction material.

[0019] Characteristics of the present invention are present in points ofusing the phenolic resin in which the ratio (o/p ratio) of theortho-bonding to the para-bonding at the methylene bonding is controlledto be in the specified range and containing the specified quantity ofthe silicone-based rubber component. As for the silicone-based rubbercomponent, mentioned is a compound of, preferably, an organopolysiloxanehaving a silanol group in each terminal of the molecule expressed by theabove-described general formula (1) and a crosslinking agent for silanolcondensation. On this occasion, the silicon-based rubber having aspecified viscosity is preferable.

[0020] The phenolic resin composition according to the present inventionis stable against the environmental moisture change. Namely, thecomposition is slow in a hygroscopic rate and small in a gel time changequantity based on a 1%-by-weight moisture absorption. Further, thecomposition is excellent in fast curing, flexibility and heatresistance. Furthermore, since the composition is excellent inflexibility, when used as a friction material for a brake and the like,the composition is excellent in vibration absorption and brake squealcharacteristics. Therefore, the composition is capable of being used forvarious types of molding materials and friction materials thereby beingextremely useful for industrial applications.

[0021] On this occasion, the ratio (o/p ratio) of the ortho-bonding tothe para-bonding at the methylene bonding in the phenolic resinaccording to the present invention and the viscosity of thesilicone-based rubber are values to be determined by methods describedin embodiments which are described on the pages that follow.

[0022] Best Mode for Carrying Out the Invention

[0023] The present invention is explained in more detail below.

[0024] A phenolic resin composition according to the present inventionis produced by adding a rubber component to a phenolic resin and mixinga resultant mixture. The phenolic resin used in the present invention issuch a resin as is produced by subjecting a phenol and an aldehyde topolycondensation.

[0025] Examples of the phenols for use in producing the phenolic resininclude phenol, cresol, xylenol, ethylphenol, propylphenol, catechol,resorcin, hydroquinone, bisphenol-A, bisphenol-F and the like. Amongthem, phenol is preferable. These phenols may be used individually or inany combination of two or more types thereof.

[0026] Examples of aldehydes include formaldehyde, paraformaldehyde,benzaldehyde and the like. These aldehydes may be used individually orin any combination of two or more types thereof. As for a catalyst: tobe used at the time of reaction of the phenol and the aldehyde, ametallic salt such as zinc acetate or the like and an acid such asoxalic acid, hydrochloric acid, sulfuric acid, diethyl sulfate,paratoluene sulfonic acid or the like can be used either individually orin any combination of two or more types thereof. Ordinarily, a quantityof the catalyst to be used is from 0.01 part by weight to 5 parts byweight based on 100 parts by weight of the phenol.

[0027] As for an effective way to enhance the o/p ratio in the phenolicresin, mentioned is a method in which paraformaldehyde is used as analdehyde and a catalyst of a divalent metallic salt of manganese,magnesium, zinc or the like is used whereupon a pH of a reaction systemis set to be from 4 to 7 and a reaction temperature is controlled to bein a range of from 100° C. to 160° C.

[0028] In the phenolic resin to be used in the present invention, theratio (o/p ratio) of the ortho-bonding to the para-bonding at themethylene bonding in the resin is from 2 to 9 and, preferably, from 2.5to 7. When the o/p ratio is less than 2, the curing rate is notsufficiently fast, which generates a difference between curing ratesbefore and after a moisture is absorbed thereby causing a variance inmolding property. On this occasion, though depending on situations, ayield at the time of molding can be deteriorated. In this connection,the range of the o/p ratio of from 2 to 9 determined by the methoddescribed in the embodiments according to the present inventionapproximately corresponds to that of from 4.9 to 22 determined by themethod by means of an infrared absorption spectrum described in JapanesePatent Laid-Open No. 071497/1999.

[0029] For example, when a hygroscopic rate of the phenolic resincomposition containing the curing agent is more than 1% by weight/hrunder conditions of 25° C. and 60% relative humidity (RH), there is adanger that the curing rate may be changed in accordance with theenvironmental moisture change while the composition is stored. Further,when a gel time change quantity (second at 150° C.) of the phenolicresin composition containing the curing agent based on a 1%-by-weightmoisture absorption comes to be more than 10 seconds, it is conceivablethat the deterioration of a yield of molded products or variance ofperformances of the molded articles is brought about. Furthermore, whena resin having the o/p ratio of more than 9 is used, at the time ofmolding, insufficient degassing due to fast curing of a surface of themolded product is likely to cause a bulge therein whereupon moldingbecomes difficult.

[0030] By using a resin having the o/p ratio of from 2 to 9 as thephenolic resin and, also, containing a specified rubber componenttherein, a molded product which is small in difference between curingrates before and after being affected by the environmental moisture,namely, absorbing the moisture, fast in the curing rate at the time ofmolding and excellent in flexibility, vibration absorption and heatresistance can be obtained. It is considered that this fact is based ona molecular structure thereof which has become difficult to be affectedby the environmental moisture.

[0031] The rubber component to be used in the present invention is asilicone-based rubber. As for the silicone-based rubber, a compound offrom 85% by weight to 99% by weight of an organopolysiloxane having asilanol group at each terminal of a molecule thereof and from 1% byweight to 15% by weight of a crosslinking agent for silanol condensationis preferable. When the crosslinking agent for silanol condensation isless than 1% by weight, crosslinking of the silicone-based rubberbecomes insufficient whereupon improvement effects of flexibility andvibration absorption are impaired; therefore, this case is unfavorable,whereas when the crosslinking agent for silanol condensation is morethan 15% by weight, heat resistance is decreased; therefore, this caseis also unfavorable.

[0032] The above-described favorable silicone-based rubber component isprepared by adding an organopolysiloxane having a silanol group at eachterminal of the molecule thereof and a silicone-based emulsifier to aheat-melted phenolic resin and, then, adding the crosslinking agent forsilanol condensation and the catalyst for silanol condensation to aresultant mixture to allow a crosslinking reaction to take place in thephenolic resin. As for the organopolysiloxane having the silanol groupat each terminal of the molecule thereof, the compound expressed by theabove-described general formula (1) is preferable and a number-averagemolecular weight thereof is preferably from 1000 to 50000.

[0033] As for the crosslinking agent for silanol condensation, mentionedis a multifunctional silane compound in which three or more functionalgroups of at least one type selected from the group consisting of: analkoxy group, an acyloxy group, a ketooxime group, an alkenyloxy group,an aminooxy group, an amino group and the like are directly bonded to asilicon atom.

[0034] Specifically, examples thereof include alkoxysilanes such asmethyl trimethoxysilane, vinyl trimethoxysilane, 3-chloropropyltrimethoxys:ilane, 3-aminopropyl trimethoxysilane,tetra(n-propoxy)silane, tetra(i-propoxy)silane, vinyl triethoxysilane,methyl triethoxysilane and the like, ketooximesilanes such as methyltris(dimethyloxime)silane, methyl tris(methyl ethyl ketooxime)silane andthe like, acyloxysilanes such as vinyl triacetoxysilane, methyltriacetoxysilane and the like, alkenyloxysilanes such as vinyltripropenyloxysilane, methyl triisobutenylsilane and the like,aminooxysilanes such as methyl tris(N,N-diamyl aminooxy)silane and thelike and amino silanes such as vinyl tris(N-butyl. amino)silane and thelike; among them, tetra(n-propoxy) silane and methyl triethoxysilane arepreferable. The above-described compounds may be used individually or inany combination of two types or more thereof.

[0035] It is preferable that from 2.6 parts by weight to 42.4 parts byweight of the organopolysiloxane having the silanol group at eachterminal of the molecule thereof and from 0.03 part by weight to 6.4parts by weight of the crosslinking agent for silanol condensation areadded to 100 parts by weight of the phenolic resin. The crosslinkingagents for silanol condensation may be used individually or in anycombination of two types or more thereof.

[0036] As for the silicone-based emulsifiers, there is no particularlimitations and one type or any combination of two types or more ofknown silicon-based emulsifiers may be used. As for a preferablesilicone-based emulsifier, mentioned is a modified silicone oil, havingan epoxy group and/or a polyoxyalkylene group at a side chain thereof,which is expressed by the following general formula (2):

[0037] wherein

[0038] R¹, R² are same with or different from each other and eachindividually represents a divalent hydrocarbon of from C₂ to C₅;

[0039] POA represents a polyoxyalkylene group which is an adduct ofethylene oxide and/or propylene oxide;

[0040] x represents an integer of from 200 to 990; and

[0041] the general formula satisfies that y+z=10˜800 and, at the sametime, x+y+z<1000.

[0042] A molecular weight of the modified silicone oil to be used asthis emulsifier, namely, values of x, y and z in the above-describedgeneral formula (2) or a chain length of the polyoxyalkylene group isnot particularly limited, but there exists a characteristic that, whenthe value of z (number of polyoxyalkylene group) is increased and,accordingly, the chain length becomes longer, compatibility of theorganopolysiloxane having the silanol group at each terminal of themolecule thereof with the phenolic resin is enhanced and, accordingly, adispersion particle size of the silicone-based rubber contained in theresin becomes minute, whereas, when the value of z is decreased and,accordingly, the chain length becomes shorter, the compatibility isdecreased. In other words, by appropriately selecting the values of x, yand z, the particle size of the silicone-based rubber dispersed in thephenolic resin can be controlled to be in a range of from 0.1 μm to 10μm.

[0043] A quantity of the silicone-based emulsifier to be added is notparticularly limited, but the quantity is preferably from 0.01 part byweight to 30 parts by weight based on 100 parts by weight of thephenolic resin. When the quantity is less than 0.01 part by weight, itbecomes difficult to control the particle size of the silicone-basedrubber in the phenolic resin within a range of from 0.1 μm to 10 μm.Further, when the quantity is more than 30 parts by weight, a productioncost is increased; this case is unfavorable.

[0044] The catalysts for silanol condensation are not particularlylimited and one type or a combination of two types or more of knowncatalysts can be used. Namely, an organic tin compound, an organic zinccompound, an organic cobalt compound and the like which have been usedas ever for producing the silicone-based rubber are mentioned, and,among them, the organic tin compound is preferable.

[0045] Specifically, mentioned are organic tin compounds such asdibutyltin dilaurate, dibutyltin diacetate, tin oleate, tin naphthenateand the like, and, among them, dibutyltin diacetate is preferable. It ispreferable that from 0.1 part by weight to 5 parts by weight of any oneof these catalysts for silanol condensation is added to 100 parts byweight of the organopolysiloxane having the silanol group at eachterminal of the molecule thereof.

[0046] The phenolic resin composition according to the present inventioncontains from 3% by weight to 30% by weight of the above-describedrubber component based on from 70% by weight to 97% by weight of thephenolic resin. When a content of the rubber component is less than 3%by weight, the friction material having flexibility which is one ofcharacteristics of the present invention can not be obtained, whereas,when the content is more than 30% by weight, flowability is decreased todeteriorate an appearance of a molded product or to decrease mechanicalstrength; this case is unfavorable.

[0047] A viscosity of the silicone-based rubber at 50° C. is preferablyfrom 5000 mm²/sec to 200000 mm²/sec, and, more preferably, from 10000mm²/sec to 100000 mm²/sec. When the viscosity thereof is less than 5000mm²/sec, the silicone-based rubber is separated and deposited on asurface of the resin; this case is unfavorable because there is a dangerof giving a detrimental effect to the flowability and the like. Further,when the viscosity thereof is more than 200000 mm²/sec, there exists adrawback that a deterioration of heat resistance is prompted to causethe friction material using the composition to generate brake squeal andthe like; this case is also unfavorable.

[0048] The phenolic resin composition according to the present inventionmay concurrently use other rubber components within a scope of notdamaging the object of the present invention so long as theabove-described ratio of the phenolic resin and the silicone-basedrubber is held. Examples of other rubber components which mayconcurrently be used include NBR, acryl rubber, styrene-butadiene rubber(SBR), butadiene rubber (BR), chloroprene rubber (CR), an elastomercontaining an acrylic acid ester and the like.

[0049] When the phenolic resin composition according to the presentinvention is used as a molding material, the composition is used byadding a curing agent. Examples of the curing agents includehexamethylenetetramine, various types of epoxy compounds each having twoor more functionalities, isocyanates, a trioxane, a cyclic formal andthe like. Among them, when curing property, heat resistance and the likeare taken into consideration, hexamethylenetetramine is preferable. Whenhexamethylenetetramine is used as the curing agent, a quantity thereofto be added is from 3 parts by weight to 20 parts by weight and,preferably, from 7 parts by weight to 15 parts by weight based on 100parts by weight of the phenolic resin composition. When the quantity isless than 3 parts by weight, curing of the resin is insufficient,whereas, when the quantity is more than 20 parts by weight,decomposition gas of hexamethylenetetramine causes a molded product togenerate a bulge, a crack and the like therein.

[0050] The phenolic resin composition according to the present inventionobtained in such a manner as described above is fast curable, excellentin flexibility, vibration absorption and heat resistance and, further,is stable against the environmental moisture change. Specifically, thehygroscopic rate thereof is at most 1% by weight/hr at 25° C. and 60%relative humidity (RH).

[0051] Examples of applications of the phenolic resin compositionaccording to the present invention include a starting material for amolding material, a binder for organic fibers, a compounding agent forrubber, a binder for a grinding material, a binder for a frictionmaterial, a binder for inorganic fibers, a covering agent for anelectronic/electric device, a binder for a sliding material, a rawmaterial for an epoxy resin, a curing agent for an epoxy resin and thelike. Among them, the binder for the friction material is specifically afavorable application.

[0052] The friction material composition is prepared by mixing a basematerial for molding into the phenolic resin composition containing theabove-described curing agent. On this occasion, the phenolic resincomposition containing the above-described curing agent is used as abinder for the base material for molding. Examples of such basematerials for molding include glass fibers, aramid fibers, carbonfibers, ceramic fibers, calcium carbonate, barium sulfate, molybdenumdisulfilde, magnesium oxide, alumina, graphite, organic dusts such as acashew dust and the like. These are ordinarily used as a mixture of twotypes or more.

[0053] The friction material composition contains from 1% by weight to33% by weight of the phenolic resin composition containing the curingagent according to the present invention and from 67% by weight to 99%by weight of the above-described base material for molding; preferably,the composition contains from 5% by weight to 23% by weight of theformer and from 77% by weight to 95% by weight of the latter. Thefriction material composition to be obtained by using the phenol resincomposition containing the curing agent according to the presentinvention as a binder provides a friction material which is stableagainst the environmental moisture change and, further, excellent infast curing property, flexibility, heat resistance and brake squealcharacteristics. For this reason, the friction material compositionaccording to the present invention is extremely useful as a startingmaterial for the friction material for automotive vehicles and the like.

EXAMPLES

[0054] The present invention will hereinafter be described in moredetail with reference to the following embodiments. However, they shouldnot be construed as limiting the present invention in any way. All“parts” and “%'s” in Examples and Comparative Examples are given byweight. Further, an o/p ratio and other characteristics shown inExamples are determined in accordance with methods described below.

[0055] (1) O/P Ratio

[0056] Various types of isomers of binuclear components in respect to aphenolic resin obtained in Examples and Comparative Examples aremeasured under conditions described below and calculated based on amathematical expression described below. (Binuclear component is definedas a compound in which a methylene group is bonded between two phenols).A liquid chromatography [pump: LC-10AD, available from ShimadzuCorporation; detector: UV-970, available from JASCO Corporation; column:trade name of inertsil C4 5 μm (4.6 ID×150 mm), available from GLSciences Inc.] is used.

[0057] <Measurement Conditions>

[0058] Temperature: 37° C.; sample concentration: 0.2%; loading quantityof the sample: 5 μl; wavelength: 254 nm; solvent: H₂O/CH₃CN(acetonitrile), flow rate: 1 ml/min; gradient conditions: 70/30% byvolume of a composition ratio of H₂O/CH₃CN is changed into 58/42% byvolume thereof in 12 minutes and, further, into 0/100% by volume thereofin 35 minutes and, then, held for 10 minutes. Detection time: 8.4minutes for p-p components, 10.1 minutes for o-p components and 13.7minutes for o-o components.

[0059] <Mathematical Expression>

[o/p ratio]=[(o-o)+(o-p)/2]/[(o-p)/2+(p-p)]

[0060] wherein

[0061] (o-o) and (o-p) represent quantities of an ortho-ortho bondingand an ortho-para bonding, respectively.

[0062] (2) Preparation of a Phenolic Resin Composition Containing aCuring Agent

[0063] 10 parts of hexamethylenetetramine is added to 100 parts of eachof phenolic resin compositions obtained in Examples and ComparativeExamples and a resultant mixture is pulverized by a pulverizer (type:Bantam mill AP-B, available from Hosokawa Micron Corporation) to obtain110 parts of the phenolic resin composition containing the curing agentin powder form. A pulverization screen to be used is of a Herringbonetype 0.5 mm and a pulverization operation is conducted twice to allow aparticle size of powders to be finer.

[0064] (3) Hygroscopic Rate (% by Weight/Hr.)

[0065] Each of the phenolic resin compositions containing the curingagent obtained in the preceding (2) is put in a temperature- andmoisture-controlled chamber which is controlled at 25° C. and 60% RH(relative humidity) and a period of time in which a moisture in thephenolic resin composition containing the curing agent reaches 1% byweight is measured to calculate a hygroscopic rate.

[0066] (4) Gel Time Change Quantity Based on Moisture Absorption(Second)

[0067] Each of the phenolic resin compositions containing the curingagent obtained in the preceding (2) and (3) is subjected to measurementsof gel time at 150° C. by a method defined by JIS K6909 and a valueobtained by subtracting a gel time after moisture absorption from a geltime before moisture absorption is set as a gel time change quantity.

[0068] (5) Viscosity of Silicone-Based Rubber (mm²/Sec:at 50° C.)

[0069] Each of the phenolic resin compositions containing the curingagent obtained in Examples and Comparative Examples is dissolved inacetone of as much as 4 times the weight of the composition, centrifugedfor 10 minutes at a rotation of 166.7 Sec⁻¹ by a centrifuge (type:H-200, available from Kokusan Corporation) to separate a silicone-basedrubber as an insoluble component. The above-described procedure isrepeated four times. The thus separated silicone-based rubber is putinto a vacuum drier at 80° C. and dried for one hour under a pressure of0.67 kPa or less to remove acetone. A viscosity of the resultant driedsilicone-based rubber is measured at 50° C. by a cone & plate typeviscometer (type: CV-1S, available from Toa Industry Inc.)

[0070] (6) Heat Resistance Test (Weight Change Ratio) (%)

[0071] 4.5 g of each of the phenolic resin compositions containing thecuring agent obtained by the preceding (2) is fed on a die of a curastmeter V type testing machine [available from Orientec Corporation]. Thecomposition is left to stand for two minutes in this state and, after itis confirmed that an entire resin is melted, a door is closed and,accordingly, the die is closed and, then, each composition is cured fora period of time until a maximum hardness, which is determined in (9) tobe described below, is reached to obtain about 3 g of a molded productof the resin having no air bubbles. The molded product of the resin isbaked in an oven at 220° C. for 1 hour and, then, weighed. A resultantbaked molded product of the resin is subjected to heat treatment at 300°C. for 100 hours and, then, weighed. A weight change rate is determinedby an expression described below.

[0072] <Conditions of Curast Meter for Producing Molded Product ofResin>

[0073] Temperature: 150° C.; die: P-200; amplitude angle: ±π/180 rad;and time: a period of time until a maximum hardness, which is determinedin (9) to be described below, is reached for each composition.

[0074] <Expression>

Wr=[(W1−W2)/W2]×100

[0075] wherein

[0076] Wr: weight change rate (%); W1: weight (g) after subjected toheat treatment at 300° C. for 100 hours; and W2: weight (g) after bakedat 220° C. for 1 hour.

[0077] (7) Dynamic Elastic Modulus (Pa)

[0078] Each of the phenolic resin compositions containing the curingagent obtained in the preceding (2) is dissolved in ethyl lactate toprepare a solution of a concentration of 50% by weight. The thusprepared solution is coated on an iron plate and, then, cured at 180° C.for 5 hours to prepare a film having a thickness of about 60 μm. Thethus prepared film is cut into a predetermined size and, then, subjectedto measurements by an automatic dynamic viscoelasticity measuring device[trade name: Rheovibron Type DDV-II-E, available from A & D Co., Ltd.]under conditions described below.

[0079] <Measurement Conditions>

[0080] Temperature: −100˜300° C.; heating rate: 2° C./min; interval ofmeasurements: 2° C.; initial tension: 7.5 g; load detection range: 10db; excitation frequency: 110 Hz; and semi-amplitude value of sine wave:0.016 cm.

[0081] (8) Compounding and Preforming of Friction Material

[0082] 200 g of a composition comprising 15 parts by weight of each ofthe phenolic resin compositions containing the curing agent obtained inthe preceding (2), 10 parts by weight of glass fibers, 50 parts byweight of calcium carbonate, 5 parts by weight of aramid fibers, 10parts by weight of graphite and 10 parts by weight of cashew dusts ismixed by a Henschel mixer at 2800 rotations per minute for 3 minutes. Aresultant mixture is fed into a mold having a length of 95 mm and awidth of 95 mm and, then, preformed in an appropriate shape at a roomtemperature under a pressure of 4.9 MPa.

[0083] (9) Period of Time Until a Maximum Hardness is Attained (Minute)

[0084] The preformed product obtained in the preceding (8) is fed into amold having a length of 100 mm and a width of 100 mm and, then, fullymolded at a temperature of 150° C. and under a pressure of 19.6 MPa. 8pieces of molded products are produced by different molding times,namely, 1, 3, 5, 7, 9, 11, 13 and 15 minutes. The molded products aretaken out of the mold immediately after the molded products are producedin respective predetermined molding times and Rockwell hardness thereofin a hot state (HRR) are each individually measured in accordance with amethod defined by JIS K7202. A graph showing a relationship between themolding time and the hardness is constructed and, then, a time when thehardness is gradually elevated and finally reaches a peak is read fromthe graph and set as a period of time until a maximum hardness isreached.

[0085] (10) Molding and Rockwell Hardness (HRS) of Friction Material

[0086] Each of the preformed products obtained in the preceding (8) isfully molded under such conditions as being at a temperature of 150° C.,under a pressure of 19.6 Mpa and for a period of time until the maximumhardness is reached which is obtained in the preceding (9). Thereafter,the thus fully molded product is baked in an oven at 180° C. for 5 hoursand, then, Rockwell hardness thereof is measured by the method definedby JIS K7202.

[0087] (11) Appearance of Friction Material

[0088] [Moisture-Unabsorbed Article]

[0089] Using the phenolic resin composition containing the curing agentwhich has not absorbed a moisture, each of the preformed products isproduced in a same manner as in the preceding (8) and is fully molded ina same manner as in the preceding (10).

[0090] [Moisture-Absorbed Article]

[0091] Using the phenolic resin composition containing the curing agentwhich has absorbed a moisture by 1% by weight in the preceding (3), eachof the preformed products is produced in a same manner as in thepreceding (8) and is fully molded in a same manner as in the preceding(10).

[0092] Subsequently, the fully molded product is baked in an oven at180° C. for 5 hours, cooled down to a room temperature and, then,examined of an appearance thereof.

[0093] [Evaluation Criteria]

[0094] Evaluation criteria are as follows; a circle mark(∘): none ofcrackles, bulges and cracks was generated; a triangle mark (Δ):a cracklewas generated; a cross mark (×): a bulge or a crack was generated tosuch an extent as molding can not be performed.

Example 1

[0095] 100 parts of phenol, 28 parts of 80%-by-weight paraformaldehydeand 0.20 part of zinc acetate were fed into a reactor provided with astirrer, a reflux condenser and a thermometer, and a temperature of aresultant mixture was gradually increased up to 100° C. at which themixture was, then, subjected to a reflux reaction for 60 minutes.Thereafter, while the temperature inside the reactor was graduallyelevated until it reached 160° C., a second reaction and an atmosphericpressure dehydration were performed for 4 hours period and,succeedingly, a vacuum dehydration was conducted. A content was removedfrom a reactor to obtain 100 parts of the phenolic resin in a solidstate at a normal temperature. Next, the thus obtained 100 parts of thephenolic resin was heated to a temperature of 170° C. and melted.Subsequently, 10 parts of an organopolysiloxane (trade name: BY16-873,available from Dow Corning Toray Silicone Co., Ltd.) having a silanolgroup at each terminal of a molecule thereof and having a number-averagemolecular weight of 33000 expressed by the above-described generalformula (1), in which R₁ and R2 each individually represent a methylgroup, was added to a thus melted phenolic resin while being stirredand, then, further stirred for 1 hour. Next, to a thus stirred mixture,added was 1.0 part of a modified silicone oil (trade name: SF8421,available from Dow Corning Toray Silicone Co., Ltd.) expressed by thegeneral formula (2) and having both an epoxy group and an POA group and,also, having a viscosity of 3500 mm²/s at 25° C.; thereafter, a thusprepared mixture was stirred for 30 minutes. At that time, a watercontent of a thus prepared reaction liquid was 0.02% by weight whenmeasured by a Karl-Fischer moisture meter. After an ion-exchanged waterwas added to the reaction liquid such that the water content of thesolution came to be 0.2% by weight, a mixture of 0.4 part oftetra(n-propoxy) silane as a crosslinking agent for silanol condensationand 0.1 part of di-n-butyltin diacetate as a crosslinking catalyst forsilanol condensation was added to a resultant solution and stirred at170° C. for 30 minutes.

[0096] Thereafter, a resultant reaction liquid was added with 2.4parts/hr of ion-exchanged water based on 100 parts of the phenolic resincomposition and allowed to perform a crosslinking reaction of a siliconeat 170° C. for 2 hours while removing a generated condensate from asystem by distillation and, then, water remained in the system wasremoved by suction under a pressure of 1.34 kPa to obtain a phenolicresin composition having a water content of 0.05% by weight or less.

Example 2

[0097] 100 parts of phenol, 29 parts of 80%-by-weight paraformaldehydeand 0.20 part of zinc chloride were fed into a reactor similar to thatin Example 1, and a temperature of a resultant mixture was graduallyincreased up to 100° C. at which the mixture was, then, subjected to areflux reaction for 60 minutes. Thereafter, while the temperature insidethe reactor was gradually elevated until it reached 160° C., the mixturewas subjected to a second reaction and an atmospheric pressuredehydration over a 4hour period and, succeedingly, to a vacuumdehydration. A content was taken out of the reactor to obtain thephenolic resin in a solid state at a normal temperature. Then, from thethus obtained phenolic resin, obtained was a phenolic resin compositioncontaining a rubber component and having a water content of 0.05% byweight or less in a same manner as in Example 1.

Example 3

[0098] Except for performing a 2-hour stirring during an interval from atime when a mixture of a crosslinking agent for silanol condensation anda catalyst for silanol condensation was added to another time when anion-exchanged water was added, a phenolic resin composition containing arubber component and having a water content of 0.05% by weight or lesswas obtained in a same manner as in Example 1.

Example 4

[0099] Except for performing a 5-hour stirring during an interval from atime when a mixture of a crosslinking agent for silanol condensation anda catalyst for silanol condensation was added to another time when anion-exchanged water was added, a phenolic resin composition containing arubber component and having a water content of 0.05% by weight or lesswas obtained in a same manner as in Example 1.

Comparative Example 1

[0100] Except for using a phenol novolac resin (Novolac #2000, availablefrom Mitsui Chemicals, Inc.), a phenolic resin composition containing arubber component and having a water content of 0.05% by weight or lesswas obtained in a same manner as in Example 1.

Comparative Example 2

[0101] Except that 1 part of an organopolysiloxane having a silanolgroup at each terminal of a molecule thereof and having a number-averagemolecular weight of 33000 was added to the phenolic resin obtained inExample 2 such that a silicone-based rubber content was 1% by weight andthat 0.05 part of a modified silicone oil expressed by theabove-described general formula (2), having both an epoxy group and aPOA group and, further, having a viscosity of 3500 mm²/s at 25° C., wasadded and a mixture of 0.05 part of tetra(n-propoxy)silane as acrosslinking agent for silanol condensation and 0.01 part ofdi-n-butyltin diacetate as a catalyst for silanol condensation wasadded, a phenolic resin composition having a water content of 0.05% byweight or less was obtained in a same manner as in Example 1.

Comparative Example 3

[0102] 100 parts of phenol, 28 parts of 80%-by-weight paraformaldehydeand 0.25 part of zinc acetate were fed into a reactor similar to that inExample 1, and a temperature of a resultant mixture was graduallyincreased up to 110° C. at which the mixture was, then, subjected to areflux reaction for 60 minutes. Thereafter, while the temperature insidethe reactor was gradually elevated until it reached 160° C. and waterremained in a system was removed by suction under a pressure of 39.9 kPaover a 4-hour period, a second reaction was performed and, succeedingly,a vacuum dehydration was conducted. A content was taken out of thereactor to obtain the phenolic resin in a solid state at a normaltemperature. Next, a phenolic resin composition containing a rubbercomponent and having a water content of 0.05% by weight or less wasobtained from the thus obtained phenolic resin in a same manner as inExample 1.

Comparative Example 4

[0103] Except that 50 parts of an organopolysiloxane having a silanolgroup at each terminal of a molecule thereof and having a number-averagemolecular weight of 33000 was added to the phenolic resin obtained inExample 2 such that a silicone-based rubber content was 36% by weightand that 3.0 parts of a modified silicone oil expressed by theabove-described general formula (2), having both an epoxy group and aPOA group and, further, having a viscosity of 3500 mm²/s at 25° C., wasadded and a mixture of 2.5 parts of tetra(n-propoxy)silane as acrosslinking agent for silanol condensation and 0.5 part ofdi-n-butyltin diacetate as a catalyst for silanol condensation wasadded, a phenolic resin composition having a water content of 0.05% byweight or less was obtained in a same manner as in Example 1.

Comparative Example 5

[0104] 30 parts of acrylonitrile, 70 parts of 1,3-butadiene, 2.4 partsof an aliphatic soap, 0.3 part of azobisisobutylonitrile, 0.5 part oft-dodecyl mercaptan and 200 parts of water were fed into apolymerization reactor made of stainless steel and subjected to apolymerization reaction in an atmosphere of nitrogen at 45° C. for 20hours while being stirred, and the polymerization reaction wasterminated at a conversion of 90% by weight. An unreacted monomer wasremoved by reduced-pressure stripping to obtain anacrylonitrile-butadiene rubber (NBR) latex having a solid content ofabout 30% by weight. Further, a solid component was collected from thelatex, dried and subjected to measurements of contents of a1,3-butadiene unit and an acrylonitrile unit in the rubber by anelemental analysis and, as a result, the contents of the 1,3-butadieneunit and the acrylonitrile unit were 71% and 29%, respectively.

[0105] Next, 100 parts of phenol, 28 parts of 80%-by-weightparaformaldehyde and 0.20 part of zinc acetate were fed into a reactorin a same manner as in Example 1, and a temperature of a resultantsolution was gradually increased up to 100° C. at which the solutionwas, then, subjected to a reflux reaction for 60 minutes. While amixture which has been prepared by sufficiently mixing 26.7 parts of theabove-described acrylonitrile-butadiene (NBR) latex and 0.3 part of a47%-by-weight aqueous solution of sodium dodecyl diphenyletherdisulfonate (trade name: Newcol-271S, available from Nippon NyukazaiCo., Ltd.) was added to a resultant reacted solution over a 1-hourperiod, a temperature inside the reactor was gradually elevated until itreached 160° C. and, simultaneously, a resultant mixture was subjectedto an atmospheric pressure dehydration over a 4-hour period and,succeedingly, to a vacuum dehydration. Water remained in a system wasremoved by suction under a pressure of 1.34 kPa to obtain a phenolicresin composition having a water content of 0.05% by weight or less.

Comparative Example 6

[0106] Using a reactor similar to that in Example 1, first of all, 50parts of ethyl acetate was fed thereto and, next, a mixture of 75 partsof butyl acrylate, 20 parts of acrylonitrile, 2 parts of glycidylmethacrylate, 3 parts of butyl methacrylate, 1 part of2,2′-azobis-(2,4-dimethylvaleronitrile) and 50 parts of ethyl acetatewas gradually added theretoin a dropping manner over a 8-hour period inan atmosphere of nitrogen under an atmospheric pressure while ethylacetate is refluxed, and a resultant mixture was allowed to bepolymerized. Subsequently, after ethyl acetate was kept refluxed for 2hours, a polymerization was performed to obtain an ethyl acetatesolution of acrylic rubber. A solid content of this rubber solution was49% by weight. A portion of this solution was dried to obtain a polymer;a viscosity of a 5%-by-weight ethyl acetate solution of the polymer was1.5 mpas at 25° C.

[0107] Next, after 100 parts of the phenol resin obtained in Example 1and 20 parts of the above-described ethyl acetate solution of theacrylic rubber were fed to a reactor similar to that in Example 1, aresultant mixture was heat-stirred for 60 minutes while removing ethylacetate distilled at 160° C. Succeedingly, ethyl acetate, water and thelike remained in a system were removed by suction under a pressure of1.34 kPa to obtain a phenolic resin composition having a water contentof 0.05% by weight or less.

[0108] <Characteristics Evaluation>

[0109] O/p ratios of the phenolic resins, viscosities of silicone-basedrubbers, hygroscopic rates and gel time change quantities based onmoisture absorption of phenolic resin compositions each containing acuring agent which were described in Examples and Comparative Exampleswere determined. Further, as a heat resistance test of the phenolicresin compositions containing the curing agent, a weight change rateafter subjected to heat treatment and, as a flexibility evaluation,dynamic elasticity were determined. Results are shown in Table 1.

[0110] <Preparation and Evaluation of Friction Material>

[0111] Using each of the phenolic resin compositions obtained inExamples and Comparative Examples, a friction material having acompounding rates described in the preceding (8) was prepared. As anevaluation of fast curing property, determination of a maximumhardness-reaching time and,, as a flexibility evaluation of the frictionmaterial, a Rockwell hardness were determined. Results are shown inTable 1. TABLE 1 Compar- Compar- Compar- Compar- Compar- Compar- ativeative ative ative ative ative Example 1 Example 2 Example 3 Example 4Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 O/p ratios6.0 2.5 6.0 6.0 0.4 2.5 9.6 2.5 6.0 6.0 Rubber contents 9.4 9.4 9.4 9.49.4 1.0 9.4 34.4 7.4 8.9 Hygroscopic rates 0.60 0.86 0.63 0.70 5.00 1.000.50 0.95 0.75 0.72 (% by weight/hr) Gel times (at 150° C. :second) 4556 46 48 106 58 33 62 48 47 Gel times after 1%-by-weight 41 50 41 42 9150 31 55 36 37 moisture absorption (at 150° C. :second) Gel time changequantities 4.0 6.0 5.0 6.0 15.0 8.0 2.0 7.0 12.0 10.0 based on a1%-by-weight moisture absorption (at 150° C. :-second) Viscosities ofSilicone-based 20000 18000 70000 100000 50000 20000 30000 30000 — —rubbers (mm²/sec) Heat resistance test; weight −23 −22 −25 −29 −25 −33−27 −30 −39 −34 change rates (%) Maximum hardness reaching 5 7 5 5 10 7— 7 5 5 times (minute) Appearances of friction ∘ ∘ ∘ ∘ ∘ ∘ x Δ ∘ ∘materials which have not absorbed moisture Appearances of friction ∘ ∘ ∘∘ Δ ∘ x Δ Δ ∘ materials which have absorbed moisture by 1% by weightRockwell hardness (HRS) 91 90 92 93 92 108 — 79 82 102 Dynamic elasticmodulus (Pa) 100° C. (E′) 2.59 × 10⁹ 2.54 × 10⁹ 2.62 × 10⁹ 2.67 × 10⁹2.67 × 10⁹ 3.91 × 10⁹ 2.61 × 10⁹ 2.02 × 10⁹ 2.19 × 10⁹ 3.17 × 10⁹ 200°C. (E′) 2.16 × 10⁹ 2.00 × 10⁹ 2.16 × 10⁹ 2.19 × 10⁹ 2.05 × 10⁹ 3.08 ×10⁹ 1.98 × 10⁹ 1.33 × 10⁹ 1.75 × 10⁹ 2.41 × 10⁹ 300° C. (E′) 1.57 × 10⁹1.31 × 10⁹ 1.60 × 10⁹ 1.60 × 10⁹ 1.68 × 10⁹ 2.67 × 10⁹ 1.40 × 10⁹ 8.07 ×10⁸ 1.54 × 10⁹ 2.05 × 10⁹

[0112] <Observation of Examples>

[0113] As is apparent from Table 1, the phenolic resin compositionsobtained by Examples 1 to 4 having an appropriately high o/p ratio andcontaining a specified quantity of a specified rubber component areexcellent in flexibility due to their low values of Rockwell hardnessand dynamic elastic modulus (E′), and also heat resistance due to theirlow weight change rates after heat treatment. Further, due to theirshort gel times and their short maximum hardness reaching times ofRockwell hardness in a heated state, they are excellent in fast curingproperty. Furthermore, due to their small hygroscopic rates and smallgel time change quantities based on a 1%-by-weight moisture absorption,they are stable against an environmental moisture change.

[0114] On the other hand, the phenolic resin composition obtained inComparative Example 1, in which the o/p ratio is lower than a range ofthat of the present invention, contains rubber component thereby beingfavorable in flexibility and heat resistance; however, the resincomposition has a large hygroscopic rate and a large gel time changequantity based on a 1%-by-weight moisture absorption thereby beingunstable against an environmental moisture and, further, it was noticedthat a crack was generated in a friction material which has been moldedby using the resin composition after absorbed moisture. ComparativeExample 2, in which the rubber content is smaller than a range of thatof the present invention, has higher Rockwell hardness and dynamicelastic modulus thereby lacking in flexibility and, further, has a largeweight change rate by heat treatment thereby being inferior in heatresistance. Comparative Example 3, in which the o/p ratio is higher thana range of that of the present invention, generated a bulge by gas atthe time of molding thereby being inferior in appearance of an obtainedfriction material. Comparative Example 4, in which the rubber content islarger than a range of that of the present invention, generated a crackin an obtained friction material. Comparative Examples 5 and 6, in whichother rubber components than the silicone-based rubber were used, eachshowed a large weight change rate by heat treatment thereby beinginferior in heat resistance and, further, showed a large gel timequantity change based on a 1%-by-weight moisture absorption therebybeing unstable against the environmental moisture change.

1. A phenolic resin composition containing from 70% by weight to 97% byweight of a phenolic resin and from 3% by weight to 30% by weight of asilicone-based rubber component, characterized in that a ratio (o/pratio) of an ortho-bonding to a para-bonding at a methylene bonding inthe phenolic resin is from 2 to
 9. 2. The phenolic resin composition asset forth in claim 1, characterized in that a viscosity of asilicone-based rubber is from 5000 mm²/sec to 200000 mm²/sec at 50° C.3. The phenolic resin composition as set forth in claim 1, characterizedin that a silicone-based rubber is a compound of from 85% by weight to99% by weight of an organopolysiloxane having a silanol group in eachterminal of a molecule of the silicone-based rubber and from 1% byweight to 15% by weight of a crossliking agent for silanol condensation.4. The phenolic resin composition as set forth in claim 3, characterizedin that the organopolysiloxane having the silanol group at each terminalof the molecule is expressed by a general formula (1):

wherein R₁ and R₂ are same with or different from each other and eachindividually represent a monovalent hydrocarbon group, an alkyl groupselected from the group consisting of a methyl group, an ethyl group, apropyl group and a butyl group, an aryl group selected from the groupconsisting of a phenyl group and a xylyl group, or a halogenatedmonovalent hydrocarbon selected from the group consisting of aγ-chloropropyl group and a 3,3,3-trifluoropropyl; and n represents aninteger of from 4 to
 675. 5. The phenolic resin composition as set forthin claim 3, wherein the crosslinking agent for silanol condensation is amultifunctional silane compound in which three or more functional groupsof at least one type selected from the group consisting of an alkoxygroup, an acyloxy group, a ketooxime group, an alkenyloxy group, anaminooxy group and an amino group are directly bonded to a silicon atom.6. A phenolic resin composition comprising 100 parts by weight of thephenolic resin composition as set forth in claim 1 and from 3 parts byweight to 20 parts by weight of hexamethylenetetramine.
 7. The phenolicresin composition as set forth in claim 6, wherein a hygroscopic rate at25° C. and a 60% relative humidity is 1% by weight/hr or less.
 8. Thephenolic resin composition as set forth in claim 6, wherein a gel timechange quantity based on a 1%-by-weight moisture absorption is 10seconds or less.
 9. A friction material composition comprising from 1%by weight to 33% by weight of the phenolic resin composition as setforth in claim 6 and from 67% by weight to 99% by weight of a moldingbase material.